There is never a wrong time to invest in mutual funds for retirement. So, if you're still looking for the best mutual funds, the Zacks Mutual Fund Rank can be a great guide.

How can you tell a good mutual fund from a bad one? It's pretty basic: if the fund is diversified, has low fees, and shows strong performance, it's a keeper. Of course, there's a wide range, but using the Zacks Mutual Fund Rank, we've found three mutual funds that would be great additions to any long-term retirement investors' portfolios.

Let's take a look at some of our top-ranked mutual funds with the lowest fees.

Fidelity Mid-Cap Stock Fund K (FKMCX Quick QuoteFKMCX - Free Report) : 0.73% expense ratio and 0.69% management fee. FKMCX is a Mid Cap Blend mutual fund, and usually features a portfolio with stocks of various styles and sizes, allowing for diversification within a strategy that focuses on mid cap companies. FKMCX has achieved five-year annual returns of an astounding 12.74%.

John Hancock Discipline Value Mid Cap I (JVMIX Quick QuoteJVMIX - Free Report) : 0.87% expense ratio and 0.71% management fee. JVMIX is a Mid Cap Value mutual funds that aims to target medium-sized companies that possess strong value and income opportunities for investors. JVMIX, with annual returns of 12.76% over the last five years, is a well-diversified fund with a long track record of success.

Invesco Growth and Income R5 (ACGQX Quick QuoteACGQX - Free Report) . Expense ratio: 0.49%. Management fee: 0.36%. Five year annual return: 11.72%. ACGQX is part of the Large Cap Blend section, and these mutual funds most often invest in firms with a market capitalization of $10 billion or more. By investing in bigger companies, these funds offer more stability, and are often well-suited for investors with a "buy and hold" mindset.

There you have it. If your financial advisor had you put your money into any of our top-ranked funds, then they've got you covered. If not, you may need to talk.